With the development of information communication technology, a variety of wireless communication technologies are developing. Among them, WLAN is technology, enabling wireless access to an Internet at specific service providing areas, such as homes, companies or airplanes, using portable terminals, such as a personal digital assistant (PDA), a laptop computer and a portable multimedia player (PMP) on the basis of radio frequency technology.
Recently, as the spread of equipment related to WLAN is increasing, users who use portable terminals, such as laptop computers, can process their tasks through improved mobility. For example, users can move their laptop computers from their desks to the conference rooms and participate in a conference. Even in this case, they can fetch data, etc. while keeping access to a local network. Users may also access an Internet through one or more modems or gateways included in their local networks although there is no wired connection. In a similar way, a person who goes on a business trip may access his e-mail account using his portable terminal without a special difficulty, read received e-mails or write e-mail, and send the written e-mails.
The WLAN technology in its early stages was to support the rate of 1˜2 Mbps through frequency hopping, band spreading, infrared communication, etc. using the frequency of 2.4 GHz through IEEE 802.11. With the recent development of wireless communication technology, it can support a maximum rate of 54 Mbps by applying WLAN to orthogonal frequency division multiplexing (OFDM) technology, etc. In addition,
In IEEE 802.11, wireless communication technologies for the improvement of Quality of Service (QoS), access point (AP) protocol compatibility, security enhancement, radio resource measurement, wireless access in vehicular environment, fast roaming, a mesh network, inter-working with external network, wireless network management, etc. have been developed and commercialized or are now developing.
In IEEE 802.11, a basic service set (BSS) refers to a collection of stations (STAs) that have realized successful synchronization. Further, a basic service area (BSA) refers to an area, including members constituting a BSS. The BSA may differ depending on the propagation characteristic of a radio medium, and has an unclear boundary a little. The BSS can be basically classified into two configurations, an independent BSS (IBSS) and an infra-structured BSS. The former constitutes a self-contained network, and refers to a BSS whose access to a distribution system (DS) is not allowed. The latter includes one or more APs, DSs, etc., and generally refers to a BSS in which an AP is employed in all communication processes, including communication between stations.
According to a WLAN communication procedure it its early stages, in the infra-structured BSS, it was necessarily required that data pass through an AP for data transmission, while not allowing the direct transmission of data between Non-AP STAs. However, in recent years, for improved efficiency of wireless communication, the infra-structured BSS supports DLS between Non-AP STAs. Accordingly, in a BSS supporting the QoS, that is, a Quality-of-Service basic service set (QBSS) consisting of a Quality-of-Service station (QSTA) and a Quality-of-Service access point (QAP), Non-AP STAs can set up a direct link and directly communicate with each other through the direct link without passing through a QAP.